STOP! If you're just getting started writing tests, have a look at Test::Simple first. This is a drop in replacement for Test::Simple which you can switch to once you get the hang of basic testing.

The purpose of this module is to provide a wide range of testing utilities. Various ways to say "ok" with better diagnostics, facilities to skip tests, test future features and compare complicated data structures. While you can do almost anything with a simple ok() function, it doesn't provide good diagnostic output.

If you don't know how many tests you're going to run, you can issue the plan when you're done running tests.

$number_of_tests is the same as plan(), it's the number of tests you expected to run. You can omit this, in which case the number of tests you ran doesn't matter, just the fact that your tests ran to conclusion.

$test_name is a very short description of the test that will be printed out. It makes it very easy to find a test in your script when it fails and gives others an idea of your intentions. $test_name is optional, but we very strongly encourage its use.

undef will only ever match undef. So you can test a value agains undef like this:

is($not_defined, undef, "undefined as expected");

(Mnemonic: "This is that." "This isn't that.")

So why use these? They produce better diagnostics on failure. ok() cannot know what you are testing for (beyond the name), but is() and isnt() know what the test was and why it failed. For example this test:

The second argument is a regular expression. It may be given as a regex reference (i.e. qr//) or (for better compatibility with older perls) as a string that looks like a regex (alternative delimiters are currently not supported):

like( $got, '/expected/', 'this is like that' );

Regex options may be placed on the end ('/expected/i').

Its advantages over ok() are similar to that of is() and isnt(). Better diagnostics on failure.

Due to how subtests work, you may omit a plan if you desire. This adds an implicit done_testing() to the end of your subtest. The following two subtests are equivalent:

subtest 'subtest with implicit done_testing()', sub {
ok 1, 'subtests with an implicit done testing should work';
ok 1, '... and support more than one test';
ok 1, '... no matter how many tests are run';
};
subtest 'subtest with explicit done_testing()', sub {
ok 1, 'subtests with an explicit done testing should work';
ok 1, '... and support more than one test';
ok 1, '... no matter how many tests are run';
done_testing();
};

Sometimes you just want to say that the tests have passed. Usually the case is you've got some complicated condition that is difficult to wedge into an ok(). In this case, you can simply use pass() (to declare the test ok) or fail (for not ok). They are synonyms for ok(1) and ok(0).

These simply use the given $module and test to make sure the load happened ok. It's recommended that you run use_ok() inside a BEGIN block so its functions are exported at compile-time and prototypes are properly honored.

Similar to is(), except that if $got and $expected are references, it does a deep comparison walking each data structure to see if they are equivalent. If the two structures are different, it will display the place where they start differing.

is_deeply() compares the dereferenced values of references, the references themselves (except for their type) are ignored. This means aspects such as blessing and ties are not considered "different".

is_deeply() currently has very limited handling of function reference and globs. It merely checks if they have the same referent. This may improve in the future.

If you pick the right test function, you'll usually get a good idea of what went wrong when it failed. But sometimes it doesn't work out that way. So here we have ways for you to write your own diagnostic messages which are safer than just print STDERR.

Sometimes running a test under certain conditions will cause the test script to die. A certain function or method isn't implemented (such as fork() on MacOS), some resource isn't available (like a net connection) or a module isn't available. In these cases it's necessary to skip tests, or declare that they are supposed to fail but will work in the future (a todo test).

For more details on the mechanics of skip and todo tests see Test::Harness.

The way Test::More handles this is with a named block. Basically, a block of tests which can be skipped over or made todo. It's best if I just show you...

If the user does not have HTML::Lint installed, the whole block of code won't be run at all. Test::More will output special ok's which Test::Harness interprets as skipped, but passing, tests.

It's important that $how_many accurately reflects the number of tests in the SKIP block so the # of tests run will match up with your plan. If your plan is no_plan $how_many is optional and will default to 1.

It's perfectly safe to nest SKIP blocks. Each SKIP block must have the label SKIP, or Test::More can't work its magic.

You don't skip tests which are failing because there's a bug in your program, or for which you don't yet have code written. For that you use TODO. Read on.

With a todo block, the tests inside are expected to fail. Test::More will run the tests normally, but print out special flags indicating they are "todo". Test::Harness will interpret failures as being ok. Should anything succeed, it will report it as an unexpected success. You then know the thing you had todo is done and can remove the TODO flag.

The nice part about todo tests, as opposed to simply commenting out a block of tests, is it's like having a programmatic todo list. You know how much work is left to be done, you're aware of what bugs there are, and you'll know immediately when they're fixed.

Once a todo test starts succeeding, simply move it outside the block. When the block is empty, delete it.

With todo tests, it's best to have the tests actually run. That way you'll know when they start passing. Sometimes this isn't possible. Often a failing test will cause the whole program to die or hang, even inside an eval BLOCK with and using alarm. In these extreme cases you have no choice but to skip over the broken tests entirely.

The syntax and behavior is similar to a SKIP: BLOCK except the tests will be marked as failing but todo. Test::Harness will interpret them as passing.

If it's something the user might not be able to do, use SKIP. This includes optional modules that aren't installed, running under an OS that doesn't have some feature (like fork() or symlinks), or maybe you need an Internet connection and one isn't available.

If it's something the programmer hasn't done yet, use TODO. This is for any code you haven't written yet, or bugs you have yet to fix, but want to put tests in your testing script (always a good idea).

The use of the following functions is discouraged as they are not actually testing functions and produce no diagnostics to help figure out what went wrong. They were written before is_deeply() existed because I couldn't figure out how to display a useful diff of two arbitrary data structures.

Sometimes the Test::More interface isn't quite enough. Fortunately, Test::More is built on top of Test::Builder which provides a single, unified backend for any test library to use. This means two test libraries which both use Test::Builder can be used together in the same program.

If you simply want to do a little tweaking of how the tests behave, you can access the underlying Test::Builder object like so:

If all your tests passed, Test::Builder will exit with zero (which is normal). If anything failed it will exit with how many failed. If you run less (or more) tests than you planned, the missing (or extras) will be considered failures. If no tests were ever run Test::Builder will throw a warning and exit with 255. If the test died, even after having successfully completed all its tests, it will still be considered a failure and will exit with 255.

So the exit codes are...

0 all tests successful
255 test died or all passed but wrong # of tests run
any other number how many failed (including missing or extras)

If you use utf8 or other non-ASCII characters with Test::More you might get a "Wide character in print" warning. Using binmode STDOUT, ":utf8" will not fix it. Test::Builder (which powers Test::More) duplicates STDOUT and STDERR. So any changes to them, including changing their output disciplines, will not be seem by Test::More.

The work around is to change the filehandles used by Test::Builder directly.

String overloaded objects are compared as strings (or in cmp_ok()'s case, strings or numbers as appropriate to the comparison op). This prevents Test::More from piercing an object's interface allowing better blackbox testing. So if a function starts returning overloaded objects instead of bare strings your tests won't notice the difference. This is good.

However, it does mean that functions like is_deeply() cannot be used to test the internals of string overloaded objects. In this case I would suggest Test::Deep which contains more flexible testing functions for complex data structures.

This is a case of convergent evolution with Joshua Pritikin's Test module. I was largely unaware of its existence when I'd first written my own ok() routines. This module exists because I can't figure out how to easily wedge test names into Test's interface (along with a few other problems).

The goal here is to have a testing utility that's simple to learn, quick to use and difficult to trip yourself up with while still providing more flexibility than the existing Test.pm. As such, the names of the most common routines are kept tiny, special cases and magic side-effects are kept to a minimum. WYSIWYG.